Update multiple fields based on condition in aggregation pipeline MongoDB Atlas trigger - mongodb

Question

I have the following pipeline that calculate the rank (sort) according to the score when the flag update is set to true:
const pipeline = [
{$match: {"score": {$gt: 0}, "update": true}},
{$setWindowFields: {sortBy: {"score": -1}, output: {"rank": {$denseRank: {}}}}},
{$merge: {into: "ranking"}}
];
await ranking_col.aggregate(pipeline).toArray();
What i do next is to set the rank to 0 when the update flag is set to false:
ranking_col.updateMany({"update": false}, {$set: {"rank": parseInt(0, 10)}});
One of my document looks like this :
{
"_id": "7dqe1kcA7R1YGjdwHsAkV83",
"score": 294,
"update": false,
"rank": 0,
}
I want to avoid the extra updateMany call and do the equivalent inside the pipeline. MongoDB support back then told me to use the $addFields flag this way :
const pipeline = [
{$match: {"score": {$gt: 0}, "update": true}},
{$setWindowFields: {sortBy: {"score": -1}, output: {"rank": {$denseRank: {}}}}},
{$addFields: {rank: {$cond: [{$eq: ['$update', false]},parseInt(0, 10),'$rank']}}},
{$merge: {into: "ranking"}}
];
This is not working in my Atlas Trigger.
Can you please correct my syntax or tell me a good way to do so ?

Answer 1

This aggregation pipeline isn't particularly efficient (a fair amount of work in "$setWindowFields" gets thrown away - more comments about this below), but I think it does what you want. Please check to make sure it's correct as I don't have complete understanding of the collection, its use, etc.
N.B.: This aggregation pipeline is not very efficient because:
It processes every document. There's no leading "$match" to filter documents.
Because of 1., "$setWindowFields" has to "partitionBy": "$update" and sort/rank the "update": false partition and "$and": ["update": true, {"$lte": ["score", 0]}] docs even though it is irrelevant.
All the irrelevant work is thrown away by just setting the "update": false" partition's "rank" to 0 and then excluding all the "$and": ["update": true, {"$lte": ["score", 0]}] documents from the "$merge".
In a large collection, your original two-step update may likely be more efficient.
db.ranking.aggregate([
{
"$setWindowFields": {
"partitionBy": "$update",
"sortBy": {"score": -1},
"output": {
"rank": {"$denseRank": {}}
}
}
},
{
"$set": {
"rank": {
"$cond": [
"$update",
"$rank",
0
]
}
}
},
{
"$match": {
"$expr": {
"$not": [{"$and": ["$update", {"$lte": ["$score", 0]}]}]
}
}
},
{"$merge": "ranking"}
])
Try it on mongoplayground.net.